EvoLunch Seminar: Lora Sweeney (Institute of Science and Technology Austria)

Four-limbed movement is a shared feature across much of the vertebrate clade.Amphibians and mammals, which last shared a common ancestor ~360 million years ago,exhibit largely the same basic limb anatomy and many identical patterns of limblocomotion, including basic sensory escape and coordinated fore/hindlimb movementsfor feeding and mating. This similarity raises the fundamental question of whether a core,shared motor circuit architecture exists in the spinal cord across such large evolutionarydistances and how it may vary in register to vertebrate movement. Recent studies havedetailed neural spinal cell-type architecture in mammals, best exemplified in mice andhumans. However, a comparable atlas of the non-mammalian, limbed vertebrate spinalcordis lacking. Here, we focus on one of the most primitive amphibians, the frog Xenopuslaevis, to evaluate conservation in spinal cell-type architecture for limb locomotionbetween frogs, mice and humans. Across species, our analysis defines a core program ofcell type specification during development, which segregates spinal neurons into nearlyidentical cardinal classes and subtypes in both amphibians and mammals. This starklycontrasts with adult stages, when spinal cell-type composition across species issimilar ata coarse level but diverges at the level of subpopulations. Using spatial transcriptomics,we localize this species-divergence to the superficial dorsal spinal cord, where variantneuropeptide expression defines mammalian-specific cell types. The dorsal spinal cordthus emerges as a more recently evolved hub for sensory integration in mammals.